User login

Navigation

You are here

research

information needed

Would anyone have spec sheets for the load cell of the LIDO multijoint systemII?

I want to convert the torque readings from volts to newton-meter. I know LIDO dynamometer gives output as torque. But, our lab does not have any spec sheets or manuals, as this system is an old donated system.

Xiaodong Li's picture

On the uniqueness of measuring elastoplasticproperties from indentation

Indentation is widely used to measure material mechanical properties such as hardness, elastic modulus, and fracture toughness (for brittle materials). Can one use indentation to extract material elastoplastic properties directly from the measured force-displacement curves? Or simply, is it possible to obtain material stress-strain curves from the corresponding indentation load-displacement curves? In an upcoming paper in JMPS titled "On the uniqueness of measuring elastoplastic properties from indentation: The indistinguishable mystical materials," Xi Chen and colleagues at Columbia University and National Defense Academy, Japan show the existence of "mystical materials", which have distinct elastoplastic properties yet they yield almost identical indentation behaviors, even when the indenter angle is varied in a large range. These mystical materials are, therefore, indistinguishable by many existing indentation analyses unless extreme (and often impractical) indenter angles are used. The authors have established explicit procedures of deriving these mystical materials. In many cases, for a given indenter angle range, a material would have infinite numbers of mystical siblings, and the existence maps of the mystical materials are also obtained. Furthermore, they propose two alternative techniques to effectively distinguish these mystical materials. The study in this paper addresses the important question of the uniqueness of indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material elastoplastic properties.

Ashkan Vaziri's picture

Flexible Probes for Characterizing Surface Topology: From Biology to Technology

In nature, several species use flexible probes to actively explore their environment, and acquire important sensory information, such as surface topology and texture, water/air flow velocity, etc. For example, rats and other rodents have an array of facial vibrissae (or whiskers) with which they gather tactile information about the external world.  The complex mechanisms, by which mechanical deformations of the probe lead to neuronal activity in the animal’s nervous system are still far from being understood. This is due to the intricacy of the deformation mechanics of the flexible sensors, the processes responsible for transforming the deformation to electrical activity, and the subsequent representation of the sensory information by the nervous system. Understanding how these mechanosensory signals are transduced and extracted by the nervous system promises great insight into biological function, and has novel technological applications. To understand the mechanical aspect of sensory transduction, here we monitored the deformation of a rat’s vibrissa as it strikes rigid objects with different topologies (surface features) during locomotion, using high-speed videography. Motivated by our observations, we developed detailed numerical models to study the mechanics of such flexible probes. Our findings elucidate how active sensation with vibrissae might provide sensory information and in addition have direct implications in several technological areas. To put this in perspective, we propose strategies in which flexible probes can be used to characterize surface topology at high speeds, which is a desirable feature in several technological applications such as memory storage and retrieval. (The full article is attached)

Amit Acharya's picture

Toward averaging nonlinear dynamics

Attached is a paper outlining ideas for averaging autonomous dynamics, based on a dynamical systems point of view.

People interested in computational multiscale modeling, especially of the sequential kind, as well as nonequilibrium statistical mechanics may find these ideas useful.

fengliu's picture

From self-bending of nanofilms to fabrication of nanotubes

We demonstrate, by theoretical analysis and molecular dynamics simulation, a mechanism for fabricating nanotubes by self-bending of nanofilms under intrinsic surface stress imbalance due to surface reconstruction. A freestanding Si nanofilm may spontaneously bend itself into a nanotube without external stress load, and a bilayer SiGe nanofilm may bend into a nanotube with Ge as the inner layer, opposite of the normal bending configuration defined by misfit strain.

Lakshmana B K's picture

Fluid-Structure Interaction study on artery help needed

I am now doing my project on "Fluid-Structure Interaction study on artery", using ANSYS-9.0, I am doing 3-D FSI analysis using fluid142 & solid185 using FSI solver. I have written a macro as per the help file specified in FSI, ANSYS under coupled field approach.

Henry Tan's picture

Journal of the Mechanics and Physics of Solids, 2007

This blog focuses on the papers in Journal of Fluid Mechanics, 2007.

Is it possible to obtain (without modeling) the fracture strength of defect-free nanotubes or nanowires by tensile loading?

What boundary conditions would allow failure to occur in the gauge length and not at or near the clamps? One is not allowed (in suggesting ways of overcoming stress concentation at the clamps) to create defects in the nanotube or nanowire, to configure the region where failure will occur.  Thus, it is not possible (or is it?)  to create an analog of dog-bone specimens by, e.g., milling away part of the nanowire with a focused ion beam, etc., because this creates defects in the nanowire.

Plastic Deformation Recovery in Freestanding Nanocrystalline Aluminum and Gold Thin Films


Science 30 March 2007:
Vol. 315. no. 5820, pp. 1831 - 1834
DOI: 10.1126/science.1137580
Jagannathan Rajagopalan, Jong H. Han, M. Taher A. Saif*
In nanocrystalline metals, lack of intragranular dislocation sources leads to plastic deformation mechanisms that substantially differ from those in coarse-grained metals. However, irrespective of grain size, plastic deformation is considered irrecoverable. We show experimentally that plastically deformed nanocrystalline aluminum and gold films with grain sizes of 65 nanometers and 50 nanometers, respectively, recovered a substantial fraction (50 to 100%) of plastic strain after unloading. This recoverywas time dependent and was expedited at higher temperatures. Furthermore, the stress-strain characteristics during the next loading remained almost unchanged when strain recovery was complete.These observations in two dissimilar face-centered cubic metals suggest that strain recovery might be characteristic of other metals with similar grain sizes and crystalline packing.

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Jinglei Yang's picture

Self-healing polymers - an introduction

I'm now working on the preparation and characterization of self-healing polymers, a promising branch in materials science. The following is a general conception of this kind of materials system. (Pasted from our group website http://www.autonomic.uiuc.edu.) I may introduce some of my current work later.

Mohsin Hamzah's picture

Boundary Element Method for Hyperelastic Materials

I am interested in using the Boundary Element Method for the hyperelastic materials. The objective of this work  is to simulate the behaviour of elastomeric or rubber-like materials parts. I am now in the derivation stage, and I intened to use Ogden constitutive model with this derivation.

Ph.D. Studentships in Spacecraft Design, Dynamics and Control

The Department of Aerospace Engineering at Ryerson University has a strong and vibrant research programme involving the development of pico- and femto-satellites (weighing less than 1 kilogram) under Dr.

Arash_Kheradvar's picture

Characterization of myocardial viscoelastic behavior based on ventricular harmonic motion

Our current ability to accurately measure ventricular global contractile behavior remains unsatisfactory due to the lack of quantitative diagnostic indexes that can assess the mechanical properties of myocardial tissue.

Mohsin Hamzah's picture

ELASTOMERS

Elastomers, or rubber like materials, have many engineering applications due to their wide availability and low cost. They are also used because of their excellent damping and energy absorption characteristics, flexibility, resiliency, long service life, ability to seal against moisture, heat, and pressure, and non-toxic. It can be easily molded into almost any shape. Applications of elastomers include solid propellant, biomechanics and medical/dental, tires, gaskets, and engine mounts.

A posteriori error estimation (indication) for extended finite element methods (XFEM)

Choose a channel featured in the header of iMechanica: 

Extended finite element methods (XFEM) have been employed in computational fracture mechanics contexts since their inception in 1999. Although some work has been performed, leading to the first adaptive strategies for the generalised finite element method (GFEM), little or no work has been published on error estimation and adaptive approximations for XFEM. A first attempt at this challenging problem is published here: 

Thickness dependent critical strain in Cu films adherent to polymer substrate

For the polymer-supported metal thin films that are finding increasing applications, the critical strain to nucleate microcracks ( εc ) should be more meaningful than the generally measured rupture strain. In this paper, we develop both electrical resistance method and microcrack analyzing method to determine εc of polymer-supported Cu films simply but precisely. Significant thickness dependence has been clearly revealed for εc of the polymer-supported Cu films, i.e., thinner is the film lower is εc . This dependence is suggested to cause by the constraint effect of refining grain size on the dislocation movability.

Mohsin Hamzah's picture

Finite Element Method for Rubber or Rubber-Like Materials

Hello, I need help for using finite element method in modelling rubber or rubber-like materials?

Thanks in advance

Mohsin Hamzah's picture

Constitutive Modelling of Elastomers

Rubber or rubber-like materials, or generally elastomers, sustain large elastic deformations. The problems of such cases are non-linear, the non-linearity came from two sources, the first one due to materials, and the second is geomertrical non-linearity. Elastomers are, also, viscoelastic, i.e. time and temperature dependent.

Pages

Subscribe to RSS - research

More comments

Syndicate

Subscribe to Syndicate